30/09/2016What is Synchronous Impedance Method measurement, calculation & assumptions Circuit Globe AC/DC DC/DC Fundamentals Design Procedure for AC/DC Circuits Switching Regulator Basics and More Circuit Globe / Synchronous Machines / Synchronous Impedance Method Synchronous Impedance Method The Synchronous Impedance Method is based on the concept of replacing the effect of armature reaction by an imaginary reactance. For a synchronous generator following are the equation given below. Where, For calculating the synchronous impedance, Zs is measured and then the value of Ea is calculated. From the values of Ea and V, the voltage regulation is calculated. http://circuitglobe.com/synchronousimpedancemethod.html 1/11 com/synchronousimpedancemethod. http://circuitglobe.html 2/11 . calculation & assumptions Circuit Globe Contents: DC resistance test Open Circuit Test Short Circuit Test Calculation of Synchronous Impedance Assumptions in the Synchronous Impedance Method Measurement of Synchronous Impedance The measurement of synchronous impedance is done by the following methods.30/09/2016 What is Synchronous Impedance Method measurement. it is assumed that the alternator is star connected with the DC field winding open as shown in the circuit diagram below. They are known as DC resistance test Open circuit test Short circuit test DC resistance test In this test. the alternator is running at the rated synchronous speed. The shape is same as normal magnetization curve.html 3/11 . After setting the field current to zero. The circuit diagram is shown below. The excitation current may be increased to get 25% more than the rated voltage. This means that the loads are disconnected. the effective AC resistance per phase is obtained by multiplying the DC resistance by a factor 1. The terminal voltage Et is measured at each step.20 to 1. The value of Rt is divided by 2 to obtain a value of DC resistance per phase.C). and the field current is set to zero. http://circuitglobe.30/09/2016 What is Synchronous Impedance Method measurement.25. the field current is gradually increased step by step. The curve so obtain is called Open Circuit Characteristic (O. The linear portion of the O. and the load terminals are kept open. calculation & assumptions Circuit Globe It measures the DC resistance between each pair of terminals either by using an ammeter – voltmeter method or by using the Wheatstone’s bridge. A graph is drawn between the open circuit phase voltage Ep = Et/√3 and the field current If. Since the effective AC resistance is larger than the DC resistance due to skin effect.com/synchronousimpedancemethod. Open Circuit Test In the open circuit test for determining the synchronous impedance. A typical value to use in the calculation would be 1.75 depending on the size of the machine.C. The average of three sets of resistance value Rt is taken.C is extended to form an air gap line. Therefore.C. The alternator is then run at synchronous speed.30/09/2016 What is Synchronous Impedance Method measurement. Each ammeter should have a range greater than the rated full load value.C) and the air gap line is shown in the figure below.html 4/11 . Same as in an open circuit test that the field current is increased gradually in http://circuitglobe.com/synchronousimpedancemethod. calculation & assumptions Circuit Globe The Open Circuit Characteristic (O.C. Short Circuit Test In the short circuit test the armature terminals are shorted through three ammeters as shown in the figure below. The field current should first be decreased to zero before starting the alternator. A graph is plotted between the armature current Ia and the field current If.30/09/2016 What is Synchronous Impedance Method measurement. calculation & assumptions Circuit Globe steps and the armature current is measured at each step. The open circuit characteristics and the short circuit characteristic are drawn on the same curve.html 5/11 .com/synchronousimpedancemethod.C). This characteristic is a straight line as shown in the figure below. The value of field current If and the average of three ammeter readings at each step is taken. The field current is increased to get armature currents up to 150% of the rated value. The synchronous impedance Z S will then be equal to the open circuit voltage divided by the short circuit current at that field current which gives the rated EMF per phase. The characteristic so obtained is called Short Circuit Characteristic (S. Calculation of Synchronous Impedance The following steps are given below for the calculation of the synchronous impedance. The synchronous reactance is determined as http://circuitglobe.C. Determine the value of short circuit current Isc and gives the rated alternator voltage per phase. The flux under test conditions is the same as that under load conditions. From the above figure consider the field current If = OA that produces rated alternator voltage per phase.html 6/11 . When the O. Assumptions in the Synchronous Impedance Method The following assumptions made in the synchronous Impedance Method are given below. http://circuitglobe. The synchronous Impedance is constant The synchronous impedance is determined from the O. the open circuit voltage is AB Therefore.C.C. calculation & assumptions Circuit Globe The graph is shown below.C.C are linear.com/synchronousimpedancemethod.30/09/2016 What is Synchronous Impedance Method measurement. the synchronous impedance ZS is constant. Corresponding to this field current.C and S.C.C and S.C. It is the ratio of the open circuit voltage to the short circuit current. This value of ZS is called the linear or Unsaturated Synchronous Impedance.html 7/11 . Potier Triangle or Zero Power Factor Method http://circuitglobe.30/09/2016 What is Synchronous Impedance Method measurement. Synchronous Reactance and Synchronous Impedance 3. Voltage Regulation of a Synchronous Generator 4. This assumption introduces considerable error.com/synchronousimpedancemethod. When the armature is short circuited.ISO. this assumption is substantially true because of the uniform air gap. China leading Manufacturers. The effect of the armature reaction flux can be replaced by a voltage drop proportional to the armature current and that the armature reaction voltage drop is added to the armature reactance voltage drop. Short Circuit Ratio of a Synchronous Machine 5. For a cylindrical rotor machine. ZS is constant. the current in the armature lag the generated voltage by almost 90 degrees and hence the armature reaction is almost completely demagnetizing.com Related Terms: 1. since the open circuit characteristics coincide with the air gap line. MMF Method of Voltage Regulation 2. However. with increasing excitation the effect of saturation is to decrease ZS and the values beyond the linear part of the open circuit called as Saturated Value of the Synchronous Impedance. The magnetic reluctance to the armature flux is constant regardless of the power factor.CE. calculation & assumptions Circuit Globe It is assumed that a given value of the field current always produces the same flux. At lower excitations. Hence. this method is also called the Pessimistic method. magicray. Pcb testing Professional optical precision AOI. Regulation obtained by using a synchronous impedance method is higher than that obtained by actual loading. Terms Post Comment Related Terms MMF Method of Voltage Regulation Synchronous Reactance and Synchronous Impedance Voltage Regulation of a Synchronous Generator Working Principle of a Synchronous Motor Synchronous Condensor Zero Power Factor Characteristic (ZPFC) Excitation System of a Synchronous Machine Generator Synchronization http://circuitglobe. calculation & assumptions Circuit Globe Leave a Reply Your email address will not be published.html 8/11 .com/synchronousimpedancemethod.30/09/2016 What is Synchronous Impedance Method measurement. Required fields are marked * COMMENT NAME * EMAIL * WEBSITE I'm not a robot reCAPTCHA Privacy . 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